This project deals with the phenomenon of natural killing (NK) in humans. The investigation of specificity on NK is approached by using the cellular immunoadsorbent technique. Uninfected tumor (K562, HSB, MOLT-4) and tumor cells persistently infected with Sendai virus (SV-HEp2) are used as target monolayers. The data suggest that NK recognition sites are heterogeneous, that different types of NK cells with different specificities exist, and that individuals differ with regard to their NK cell repertoire. Further experiments to delineate the role of interferon and interferon inducers in the regulation of NK levels are carried out. Preliminary data suggest that a basal level of NK is independent of the interferon generated during the in vitro assay. Experiments with mononuclear cells derived from ascites and tumor of ovarian cancer patients are conducted to assess their NK levels. The data suggest that NK levels of cells found in the ascitic fluids and tumor are low or absent, but can be augmented by interferon in vitro. Antibody dependent cellular cytoxicity (ADCC) is also low possibly due to suppression by a subpopulation of macrophages.